Cavity Wall Insulation

Fitting cavity wall insulation is a cost effective way to improve the energy efficiency of your home.

What is cavity wall insulation?

Most homes built since 1920s were built with two layers of wall with a gap or a cavity between them. Cavity wall insulation fills this cavity. It keeps the warmth inside and also prevents condensation inside your house.

Cavity walls are filled with an insulating material. The most commonly-used materials include: mineral wool polystyrene beads.

How much can I save with cavity wall insulation?

  • Installation cost: £400-£500
  • Payback time: Less than 4 years
  • Annual saving: Up to £150

These figures are estimated. They are based on installing cavity wall insulation on a semi-detached three bedroom house.

Is cavity wall insulation suitable for my home?

Usually, your home is suitable for cavity wall insulation if:

  • The external walls are unfilled cavity walls
  • the cavity is at least 50mm wide
  • The walls of your property are in good condition
  • The external walls are not exposed to driving rain.

If unsure you can check with your local authority’s building control department, they sometimes know if your cavity walls are already insulated. You can also ask a registered installer for a boroscope inspection. Please note that if your house is less than 20 years old, its is very likely that its cavity walls are already insulated.

How is cavity wall insulation installed?

To install cavity wall insulation on your house, you need a registered installer.

The installer uses specially designed machine which drills small holes in the outside wall of your house and blows insulation in the cavity. It is a quite simple and quick procedure for a registered installer. Depending on the size of your house and the accessibility of the walls it should not take him more than half a day.

How do I find an installer?

Find a local registered installer by calling the Energy Saving Trust helpline on 0300 123 1234.

Make sure the installer is a member of the National Insulation Association (NIA), the Cavity Insulation Guarantee Agency (CIGA) or the British Board of Agrément (BBA).

Can I apply for free or discounted cavity wall insulation?

You might be eligible for free or discounted wall insulation. Check our Energy Efficiency Government Schemes page to find out more.

How can I finance cavity wall insulation?

You can finance cavity wall insulation through the new government energy efficient home improvement scheme, the Green Deal (click here to learn more and see if you are eligible) . You pay back this investment through savings on your energy bills. Another subsidy called ECO (click here) might also be available too.


Energy Saving Trust

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